Such semiconductors as AlN, GaAs, GaN, InP, Si, SiC can be formed by deposition. For the deposition, such processes as chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) are applied. In these deposition processes, a semiconductor film is formed in such a manner that a substrate is placed in a chamber in a heated state, to which source molecules are supplied, in a state of gas, to the surface to form a crystal layer on the surface of the substrate.
For these kinds of deposition processes, it is necessary to accurately control the temperature of the substrate in the chamber in order to prepare a crystal layer of intrinsic semiconductors, at a constant deposition rate, precisely, and with reproducibility. For these purposes, a heater is provided to heat the substrate, and also a monitoring device is used to measure the temperature of the substrate in the chamber, so that the heater is set based on a temperature measured by the monitor.
As described in Patent Literature 1 and Patent Literature 2, a pyrometer which watches infra-red rays emitted from heat of the substrate surface has been conventionally used as the monitor. The pyrometer is installed outside the window provided on the chamber, and infra-red rays emitted from the surface of the substrate or the surface of the semiconductor layer during the deposition are detected by the pyrometer through the glass window. Temperature monitoring by the pyrometer, however, raises the following problems.
When the infra-red rays emitted from the surface of heated substrate pass through the semiconductor layer during the film deposition process, the light passing through and the light reflected inside the semiconductor layer interfere with each other, causing fluctuation of detection output of the pyrometer. Moreover, the degree of the interference varies with the change of the film thickness of the semiconductor layer being formed. This problem has been conventionally solved in such a manner that a light emitting device is disposed outside the chamber, and the light is reflected on the semiconductor layer being deposited through the transparent window of the chamber, and the reflected light is monitored. Since the light reflecting on the semiconductor layer surface is reflected, it also interferes with the light reflected inside the semiconductor layer, as with the case of infra-red rays. The amount of light emission offset due to the interference can thus be determined, and a calibration of the infrared emission is possible, reducing the fluctuations in temperature measured by the pyrometer.
However, even if the interference of the infra-red rays detected by the pyrometer is calibrated, the temperature monitoring by the pyrometer is carried out at a place away from the surface of the substrate, generally outside the glass window of the chamber. A long distance exists between the actually heat-generating surface of the substrate and the monitoring spot, also via the glass window, and therefore, it is unavoidable to produce an error between the temperature detected by the pyrometer and the actual temperature at the surface of the substrate.
Moreover, in case the semiconductor layer and its substrate are transparent, the pyrometer really monitors the temperature of the chamber's substrate holder surface via the transparent semiconductor layer. Thus, it is difficult to detect the temperature of the semiconductor layer being deposited, directly and accurately, by such a measuring method as using a pyrometer.
Patent Literature 1 discloses also use of a thermocouple monitor to detect the temperature on the rear side of the substrate. However, since the thermocouple monitor is disposed on the rear side of the substrate, actual temperature on the surface of the substrate cannot be measured accurately. Moreover, since the heat capacity of thermocouple monitor is large, follow-up to temperature change in the chamber is not adequately made, and therefore, it is not possible to know the substrate temperature accurately.
[Patent Literature 1]    Japanese Unexamined Patent Application Publication No. 2001-289714
[Patent Literature 2]    Japanese Unexamined Patent Application Publication No. 2002-367907